SUMMARY: To reduce CO2 emission producing Ordinary Portlandcement (every ton of Portland cement accounts for roughly 850 kg CO2) the use of supplementary cementing materials (SCM’s) are becoming todays standard in the cement and construction industry. Although some SCMs are used on their own, most of them are used in combination with Portlandcement clinker.

1. Ludo Vannes Blessing
1. Introduction
To reduce CO2 emission producing Ordinary Portlandcement
(every ton of Portland cement accounts for roughly 850 kg
CO2) the use of supplementary cementing materials (SCM’s)
are becoming todays standard in the cement and construction
industry.
Although some SCMs are used on their own, most of them are
used in combination with Portlandcement clinker.
SCM’s can be divided in latent hydraulic or pozzolanic;
• limestone
• fly-ash
• GGBS – slag
• calcined marl
In all cases SCM’s / OPC blends should comply to the minimal
cement standards for making concrete.In most cases reduc-
tion of Portland cement clinker content lead to a reduced initial
strength.
GGBS (Ground Granulated Blast-furnace Slag) is a ce-
mentitious material, a by-product from the production
of iron through a blast furnace.
Silicates and alumino-silicates of calcium are the main
minerals.
Molten slag is quenched rapidly with water giving so
called granules < 5mm.
After drying these are ground in a ball mill to a fine-
ness similar to that of Portland cement.
On its own GGBS is latent hydraulic, showing poor
early strength caused by a slow hydration.
Crystalline aluminosilicate glass is formed on the sur-
face of the GGBS particles slowing down hydration,
i.e. it needs some form of activator.
Normally an alkaline or caustic solution; sodium-, po-
tassium hydroxides or sodium silicate will break up
the aluminosilicate glass layer, allowing hydration to
start.
In our quest in finding an optimum replacement of
fast setting Portlandcement we explored the effect of
adding a finer ground special GGBS containing ele-
vated amount of aluminium to a regular ground slag.
Aim was to accelerate the setting time of a pure GGBS
binder and improve its early strength develop-
ment. From different publications we learned that
fast setting cements contain C11A7.CAF2 similar to
the phases calculated from our Type II GGBS.
2. Ground Granulated Blast Furnace Slag
Chemical composition of GGBS varies depending on the
composition of the raw materials and flux agents used.
When the slag is quenched rapidly,with water or com-
pressed air, its reactivity is considerably improved.Slow
cooling means a slag is obtained without hydraulic prop-
erties.
The so called granules are than ground to a fineness sim-
ilar to that of Portlandcement and can be considered as
part replacement.
FAST SET GGBS BINDER
Abstract
To reduce CO2 emission producing Ordinary Portlandcement (every ton of Port-
land cement accounts for roughly 850 kg CO2) the use of supplementary ce-
menting materials (SCM’s) are becoming todays standard in the cement and
construction industry.
Although some SCMs are used on their own, most of them are used in combi-
nation with Portlandcement clinker.
Aim was to accelerate the setting time of a pure GGBS binder and improve
its early strength development. From different publications we learned that
fast setting cements contain C11A7.CAF2 similar to the phases calculated
from our Type II GGBS.
Keywords
GGBS (Ground Granulated Blast-furnace Slag), green and sustainable,calcium
sulfate, calcium fluoride, ettringite, early strength development, shrinkage,
setting time, isothermal reaction.
Correspondence
L.C.Vannes Blessing
Technical Developing lab
CALTRA NEDERLAND bv
Communicatieweg 21
The Netherlands
Email: caltra1@gmail.com

2. GGBS normally consist of CaO (30-50%), SiO2 (28-38%),
Al2O3 (8-24%), and MgO (1-18%).
In our study two different types are being used.Table 1
and 2 show the chemical constituents.
Aim is it to obtain a fast setting, high early strength ce-
mentious binder without the use of Portlandcement
3. Production
European standard EN 197-1 limits the amount of replace-
ment in Portland slag cement to not more than 35% .Gen-
erally this type of cement has better sulphate and chloride
resistance, and generates less heat on hydration than
Portlandcement on its own.
GGBS has a similar mineralogy as Ordinary Portlandce-
ment, and often used as part replacement of Portlandce-
ment.Its “carbon footprint” is considerably lower i.e.;
• Portland cement 850 kg/to.
• GGBS 42 kg/to.
On its own however the material is latent hydraulic and
developing poor strength, and need some form of activa-
tor.Alkali released on hydration of cement is most effective
and commonly used.Separate added non cement alkali ac-
tivators in form of sodium- or potassium oxide (Na2O -
K2O) or derivates like sodium hydroxide (NaOH),sodium
silicate (Na2SiO3)are being used.
Possible downsides in using GGBS need mentioning are ;
1. reduced availability roughly 350 Mt/y
2. increased demand to reduce carbon footprint
(cement industry)
3. forced closure of furnaces due to high energy
cost (Arcelor Mittal plans closure of two blast fur-
naces in Germany and Spain)
4. increased use of recycled steel reduce availability
Today calcium aluminate cement or calcium sulfo alumi-
nate cement are also used in combination with GGBS to
improve early strength and reactivity.
In this case we refer to earlier published studies we have
undertaken on “Amorphous Calcium Aluminate Cement”
and “Flash Calcined Alumina”.
Focus in this investigation is on developing a complete ce-
ment free binder having the same characteristics as fast
setting Portland cement. To obtain this our study is on
blending a regular available slag (Table I.) with a special
slag having a considerable higher amount of alumina (see
Table II). It is known that this type also contains a certain
amount of Calcium Fluoride.
[1] The first stage of our investigation we searched
the optimum combination of the two types to see
if we could come to a satisfactorily setting time
and early strength development.
[2] The second part of our investigation we took the
best performing blends from stage 1.and tested
the best type and addition rate of calcium sul-
fate.
[3] At the third stage of our work we made a mortar
according to EN-196 – binder:normsand ratio
1:3 parts by weight.
[4] Stage IV looked at the effect the addition of cal-
cium sulfate had on the change in volume
4. Materials and Methods
Over the years we have been involved in the devel-
opment of fast setting binders with a close eye on con-
sistency and environment. In these cases we investigated
the use of forms of calcium aluminate and calcium sulfate.
Now our goal is to propose a fast setting binder con-
sisting completely of industrial by-products – GGBS
marked RG and Type XF (Table 1 and Table 2) and addi-
tional studies were done including a residual calcium sul-
fate.(Table 3)

3. It is known that solutions in the presence of lime, alumina,
calcium sulfate reacts to lead to initial formation of differ-
ent, often complex hydrates but mainly;
• AFt (ettringite) 3CaO·Al2O3·3CaSO4·32H2O
• AFm (mono sulfo aluminate)
3CaO·Al2O3·CaSO4·12H2O and 4CaO·Al2O3·19H2O
This formation improves the early strength and acceler-
ates drying of the binder.As this chemical reaction takes
place expansion occurs, compensating drying shrinkage.
5. XRD Analysis
XRD analysis show both types of GGBS are mainly crystal-
line.GGBS XF showed a content around double amount of
Al2O3 – and significant lower amount of SiO2 – CaO is
slightly higher.
Markable is the content of calcium fluoride.
6. Experimental
The compositions tested all included both types of GGBS.
To facilitate the use we added 1% of citric acid as set re-
tarder, and 0,45% of a super plasticizing agent as water
reducer.
Testing various different ratio of these three constituents
following formulation was chosen to be tested further.
7. Strength Testing
Strength testing was done at 24 hours, 2 and 7 days on
40x40x160mm prims confectioned in compliance with EN
196-1, Methods of testing cement — Part 1: Determination
of strength. The strength results are shown in Table 4.
Mentioned formulation was mixed with 1350 gr. CEN
Standard sand EN-196-1Normsand and mixed according
the standard.

4. Noted is that a higher water/cement ratio was used.
8. Shrinkage / Expansion
In order to measure the shrinkage or expansion of the, the
mixture as mentioned were placed into 40x40x160mm
prisms according to EN196-1. These prisms were con-
nected to a micrometer, which digitally measured the lin-
ear length change every hour, and followed for 7 days and
after.The results up to 7 days are hereby presented.
9. FINDINGS
Regular GGBS marked RG showed no initial reactivity on
its own, and clearly needs an activating.
This study shows that regarding the strength development
the fine ground special form of GGBS marked XF achieved
the highest flexural and compressive strength.
Blending the two types lead to more than satisfying re-
sults.
Data of the isothermal calorimetric analysis indicate that
the addition of sulphate helps in a improving the early
strength development. Formation ettringite gave a mini-
mal expansion leading to a reduction of shrinkage. A small
retardation in set times was noticed.
Lastly, the XRD analysis of fine GGBS-XF showed pres-
ence of calcium fluoride.It is expected this contributed to
activating the regular slag used. Forming C11A7 phase is
expected to have the most impact of type XF. Grinding
this type to a finer particle size further boosted the reac-
tivity further. It increased the water consumption.
However pore structure and pore size were only margin-
ally effected, and strength development were satisfac-
tory.
10. CONCLUSIONS
In conclusion, data shows that the optimum blends are the
GGBS RG and XF types combined with anhydrous sulfate.
GGBS can be activated by Type XF. Depending on the re-
quirements the addition can be varied and depends largely
on the chemistry of the slag available.
GGBS XF + calcium sulphate outperforms in all areas,
achieving the highest compressive and flexural strengths,
and the most stable shrinkage compensation. This is con-
firmed by the amount of ettringite formed found in the
XRD analysis.
The research showed that fineness too has a significant
impact on the end result, which can only in part be com-
pensated by increasing the dosage.
In all cases it is essential to find the right equilibrium of all
components in the matrix.
Effects aimed to be achieved depend to a large extend to
the type of raw materials being used.
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